This invention relates to electron transfer systems; and, more particularly, to electron transfer systems that are driven by photo-energy.
Photo-energy driven systems for electron transfer from one chemical species to another chemical species is of great academic interest, but in recent years has evoked even more interest because of the fossil fuel energy crisis and the obvious non-renewable depletion of fossil fuels. Such depletion has sparked research in the utilization of non-depleting sources, e.g., sunlight, as the driving force for chemical reactions. It is anticipated that such reactions can produce useful products such as high energy molecules, e.g., hydrogen, oxygen, which may, themselves, be used as fuel sources. Such photo-induced reactions also hold potential for the direct production of useful chemical products.
One area that has been rather extensively investigated is the utilization of metal complexes as electron-transfer agents and catalysts to accomplish the photo-dissociation of water into its respective elements, hydrogen and oxygen. Complexes such as the ruthenium porphyrins, ruthenium diiso-cyano compounds, europium complexes, rhodium complexes, and manganese organo-complexes have all been discussed. Such patents as U.S. Pat. Nos. 4,045,315; 4,069,120; 4,094,751; 4,105,517; 4,169,030; 4,176,026; and 4,211,621, all deal with various techniques and methods of utilizing photo-energy in the conversion of water into useful forms of its elements, H.sub.2 and O.sub.2.
The principal problems encountered by investigators fall into two main areas. First, the relatively low efficiency of the chemical complexes in capturing photons and thereby having their electron's energy levels raised to a sufficient level to be available for interaction with other chemical species, i.e., electron acceptors. Second, the extremely high rate of "back-reaction" whereby any electrons which may be transferred from the photo-activated complexes to electron acceptor species, are immediately transferred back to the electron donor. Such back-reactions thereby effectively negate the useful reaction and impede the further desired dissociation of the water substrate.
Despite reports of progress in overcoming the above-noted problems as set forth in the above-noted patents, the problems of increasing the activation efficiency of the electron donor complexes and reducing the "back reaction" of electron transfer from the electron acceptor back to the electron donor, have not been satisfactorily solved.
The present invention presents an improved photo-induced electron transfer system that deals with the above-noted problems.